I've studied that proteins found in a sample as biochemical evidences for evolution. Its variation in structure and configuration can be used to date the age when that mutation occured, effectively dating the sample. But can't DNA be directly used for the process? Proteins also require transcription and translation, increasing error. I think proteins make phylogenetic detection easier, but doesn't transcription and translation give more room for error?
Yes, you are right. Proteins are specified by DNA sequences, so DNA sequencing is a more direct way to obtain essentially the same information. Note that mutation dating via DNA or proteins is approximate. It involves a lot of assumptions about continuous rates of mutation, but in fact mutation is a stochastic process and does not have a knowable continuous rate. The sequence of mutations can be determined with high confidence, but the rate can only be determined approximately.